In a wireless communication system, handover is an essential technology for providing a seamless service to a Mobile Station (MS) that moves between Base Stations (BSs). Thus, handover is also supported by a High Speed Packet Access (HSPA) system, which is a Wideband Code Division Multiple Access (WCDMA) communication system that is a widely used communication technology. Handover in the HSPA system is described below. An MS measures a DownLink (DL) subcarrier energy to noise power ratio (hereinafter, referred to as “Ec/No”), and successively performs handover for a data channel and a control channel depending on a difference between an Ec/No of a target cell and an Ec/No of a serving cell.
That is, in the HSPA system, the DL Ec/No is a criterion for handover. More particularly, at timing when the difference between the Ec/No of the target cell and the Ec/No of the serving cell is lowered to predefined threshold or less, the MS reports the Ec/No measurement result, and performs handover for Dedicated Physical Channel (DPCH) and channels related to E-DCH (Enhanced Dedicated Channel) expect E-AGCH (E-DCH Absolute Grant Channel). Additionally, at timing when the difference between the Ec/No of the target cell and the Ec/No of the serving cell is substantially similar to ‘0’, the MS reports the Ec/No measurement result and, according to a control of a Radio Network Controller (RNC), performs handover for all DL channels of a High Speed Shared Control Channel (HS-SCCH), a High Speed Physical Downlink Shared Channel (HS-PDSCH), and so forth, and E-AGCH which is one of UpLink (UL) channels.
As described above, in an HSPA system, handover for UL channels and handover for DL channels are all performed on the basis of a DL Ec/No. In other words, the handover for the UL channels is performed considering only a DL wireless environment excepting a UL wireless environment. However, in the real wireless environment, it frequently occurs that UL coverage and DL coverage are not the same as each other. Thus, there is a problem that the handover for the UL channels is performed at improper timing because the handover for the UL channels is performed on the basis of the DL wireless environment.